The invention is used in the medical field, when it is necessary to implant a prosthesis in a given area of a duct of a patient's body. More particularly, the invention may be used for the insertion of a blood filter into a vessel in order to retain blood clots which maybe present.
Devices of this type are known and described in patent application FR-A-2 657 261, for example. In general, the device comprises a tubular sheath inserted into the duct over the desired length to extend as far as the area where the prosthesis is implanted. This sheath is usually produced of a supple material so that it can adapt easily to sinuous paths; it is thus easy to position using a guide thread and an introducing tube. This device likewise comprises a control rod, suitable for sliding in the sheath and for causing the prosthesis to slide therein, which prosthesis may this be directed towards the area of implantation where it may then be expelled to the outside of the sheath to implant itself in the duct by unfolding itself there.
The checks which are usually performed after the implantation of the prosthesis, to ensure the correct insertion thereof in the duct, have shown that the prosthesis is sometimes incorrectly positioned in the duct and there is thus a risk that it will not perform its function correctly.
These problems have been observed most particularly in the field of blood filters.
Among these filters, there are those which currently have, in the unfolded position, the general form of a small frustoconical basket comprising a plurality of resilient fingers, and which may be folded back on themselves to be introduced easily into the interior of their implanting device. Filters of this type are often positioned in the inferior vena cava, by the percutaneous method Of access or by "stripping", either in the vicinity of the jugular vein (via the superior vena cava) or in the vicinity of one of the femoral veins. It is in particular in the latter case, where an introduction is performed via the femoral route, that it has been established that there is sometimes an asymmetrical opening of the filters in the vessels, even if "auto centering" filters, i.e. those which are intended to unfold themselves naturally with their longitudinal axis substantially merged with that of the vessel, are used. This incorrect opening is detrimental, particularly for filters called "definitive" or "permanent" filters, which are provided with a means of anchoring to the wall of the vessel and the position of which can thus in practice not be corrected after the opening of the filter.